1. Field of the Invention
The present invention relates to a semiconductor device and method of manufacture thereof, a circuit board and an electronic instrument.
2. Description of Related Art
As higher mounting density of semiconductor devices is demanded, bare-chip mounting is ideal. However, for bare chips, quality assurance and handling are difficult. In response to this, semiconductor devices have been developed to which Chip Scale/Size Package (CSP) technology in applied. There is no formal definition of CSP, but generally this refers to an IC package in which the package size is the same as or only very slightly larger than the chip size. The development of CSP technology is very important as high-density mounting advances. One prior art publication relating to CSP is International Patent Publication WO95/08856.
According to this, a gap is formed between a substrate having external electrodes and a semiconductor chip, and into this gap resin is injected. This resin is such as to have resilience once cured. By means of this resilient resin, stress (thermal stress) applied to the external electrodes is absorbed. It should be noted that this stress is caused by the difference in coefficient of thermal expansion between the semiconductor device and the circuit board on which the semiconductor device is mounted.
However, the resin injected between the semiconductor chip and the substrate is extremely thin, and for this reason it has not been possible adequately to absorb the thermal stress.